1. Field of the Invention
The present invention relates to optical attenuators, and more particularly to fixed optical attenuators used in optical systems.
2. Description of Related Prior Art
Optical attenuators are widely used in optical transmission systems and optical networks. Optical attenuators are passive optical components that can reduce optical power propagating in optical fibers, and may be categorized as either fixed or variable attenuators.
FIG. 9 is a cross-sectional view of a fixed optical attenuator known in the prior art. A through hole 13 is bored in the central portion of a cylindrical ferrule 14. An optical attenuation fiber 15 is inserted into the through hole 13 and is glued to the inner surface thereof. Further, a flange 18 is fixed onto the circumferential surface of the ferrule 14. This flange 18 serves to limit the movement of the ferrule within the optical attenuator in the axial and circumferential directions.
In FIG. 9, a plug housing consists of body components 19 and 20. Further, an alignment sleeve 17 is provided in the component 20. An end part of the cylindrical ferrule 14 is inserted into one end of the alignment sleeve 17 and another end part of the ferrule 14 is connected to the component 19 in such a way that the component 19 inhibits the rotation of the flange 18. An outer thread 202 of the component 20 is engaged with an inner thread 192 of the component 19, thereby providing threaded engagement to fasten the components 19, 20 together. A coupling nut 16 is rotatably mounted on the component 19 of the plug housing.
In this design, the components 19 and 20 are fastened together by threaded engagement of the inner thread 192 and the outer thread 202. However, the threaded engagement between the components 19 and 20 is not reliable after long use. Furthermore, during assembly, the component 19 and/or the component 20 must be rotated to be fastened together, in such a way that it is difficult and inefficient to assemble the optical attenuator.
Thus, it is desired to provide a fixed optical attenuator which is robust and which can be assembled easily and efficiently.